全文获取类型
收费全文 | 2690篇 |
免费 | 13篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 247篇 |
大气科学 | 168篇 |
地球物理 | 539篇 |
地质学 | 941篇 |
海洋学 | 60篇 |
天文学 | 629篇 |
综合类 | 31篇 |
自然地理 | 101篇 |
出版年
2024年 | 20篇 |
2023年 | 12篇 |
2022年 | 24篇 |
2021年 | 37篇 |
2020年 | 45篇 |
2019年 | 42篇 |
2018年 | 138篇 |
2017年 | 113篇 |
2016年 | 153篇 |
2015年 | 78篇 |
2014年 | 133篇 |
2013年 | 150篇 |
2012年 | 106篇 |
2011年 | 116篇 |
2010年 | 98篇 |
2009年 | 110篇 |
2008年 | 88篇 |
2007年 | 62篇 |
2006年 | 59篇 |
2005年 | 56篇 |
2004年 | 32篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 36篇 |
2000年 | 39篇 |
1999年 | 44篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 27篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 31篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 41篇 |
1988年 | 48篇 |
1987年 | 52篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 61篇 |
1983年 | 58篇 |
1982年 | 34篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1976年 | 12篇 |
1973年 | 12篇 |
1972年 | 14篇 |
排序方式: 共有2716条查询结果,搜索用时 15 毫秒
991.
Recent research has shown evidence of strong coupling between the atmosphere and lithosphere in coastal regions, associating abnormal atmospheric phenomena to the occurrence of strong earthquakes. Surface latent heat flux (SLHF), total column water vapor (CWV), relative humidity (RH) and total ozone column (TOC), analyzed over the epicentral region of the Denali fault earthquake of November 3, 2002, exhibit anomalous behavior that could be related to the earthquake preparatory process and its occurrence. The complementary nature of the parameters provides strong support that the anomalous values were driven by lithospheric processes, rather than other atmospheric phenomena. Due to the wide availability of remote sensing observations of atmospheric parameters, the detection of anomalies can be used to mitigate the earthquake risks. 相似文献
992.
S. Pradhan K. K. Bandyopadhyay R. N. Sahoo V. K. Sehgal R. Singh V. K. Gupta D. K. Joshi 《Journal of the Indian Society of Remote Sensing》2014,42(4):711-718
Field experiment was conducted in a sandy loam soil of Indian Agricultural Research Institute, New Delhi during the year 2011–13 to see the effect of irrigation, mulch and nitrogen on canopy spectral reflectance indices and their use in predicting the grain and biomass yield of wheat. The canopy reflectances were measured using a hand held ASD FieldSpec Spectroradiometer at booting stage of wheat. Four spectral reflectance indices (SRIs) viz. RNDVI (Red Normalized Difference Vegetation Index), GNDVI (Green Normalized Difference Vegetation Index), SR (Simple Ratio) and WI (Water Index) were computed using the spectral reflectance data. Out of these four indices, RNDVI, GNDVI and SR were significantly and positively related with the grain and biomass yield of wheat whereas WI was significantly and negatively related with the grain and biomass yield of wheat. Calibration with the second year data showed that among the SRIs, WI could account for respectively, 85 % and 86 % variation in grain and biomass yield of wheat with least RMSE (395 kg ha?1 (15 %) for grain yield and 1609 kg ha?1 (20 %) for biomass yield) and highest d index (0.95 for grain yield and 0.91 for biomass yield). Therefore it can be concluded that WI measured at booting stage can be successfully used for prediction of grain and biomass yield of wheat. 相似文献
993.
S. P. S. Kushwaha I. J. Singh Subrato Paul 《Journal of the Indian Society of Remote Sensing》2003,31(4):283-290
Remote sensing is being increasingly used for forest resource inventory as it saves time and the cost. Aerial photographs
and satellite images have been effectively utilized for forest inventory all over the world. This study highlights the application
of IRS LISS-III imagery for inventorying the stand volume in Lachchhiwala Forest Range of Siwaliks. The satellite image was
visually interpreted for forest type and density stratification. Both random as well as stratified random sampling techniques
were used to see their impact on the volume estimates. Field sampling was done in the plots of 0.1 ha size. The total growing
stock in all types of forests in the study area was estimated to be 1.87 mill.m3, of which Sal Forest accounted for 1.32 mill.m3, Sal Mixed Forest for 0.09 mill.m3, Mixed Sal Forest for 0.08 mill.m3, Miscellaneous Forest for 0.06 mill.m3 and Forest Plantations for 0.02 mill.m3. The results were compared with an independent field-based inventory carried out by forest department. The two sampling methods
were compared by ratioing of the mean of variance (gain in precision) and it was found that the timber volume estimates using
stratified random sampling technique were 15 per cent more accurate than simple random sampling. The satellite image-based
inventory using stratified random sampling was found to have about 90 per cent correspondence with the inventory done by the
Forest Department. 相似文献
994.
Extreme localised rainfall events are part of monsoon system occurring every year. Satellite data (TRMM and other geostationary
satellites) together with ground observations will be useful in providing spatial and temporal variability of atmospheric
changes. The short and long term variability is required for better understanding of the local and regional climatic conditions
through detailed modelling. Such information will play a key role in real time data analysis and dissemination system to the
disaster management groups in the country to minimize losses due to these extreme rainfall events. 相似文献
995.
In this paper we have investigated some LRS Bianchi type-V cosmologicla models representing a viscous fluid distribution with a null electromagnetic field and streaming neutrinos. Various physical and kinematical features of these models have also been explored. 相似文献
996.
A study was undertaken to evaluate the potential of RADARSAT SAR data (Standard-7 and Wide-2 beam positions) for delineating
the geomophological units in Itanagar Capital Complex of Arunachal Pradesh, India. Principal Component Analysis (PCA) has
been applied to Standard-7 and Wide-2 data with incidence angle 45° – 49° and 31 ° – 39° respectively. The resulting components
yield imagery that highlights the Geomorphological units. The area of investigation has been classified into five geomophological
units’ viz., High relief structural hills, low relief structural hills, low relief rugged hills, piedmont and intermontane
valley. The surface roughness can be observed by studying the difference of the responses from different incidence angles.
Wide-2 beam position was found to be more useful for identifying features in flat terrain, and Standard-7 beam position data
for features of high relief. 相似文献
997.
Munendra Singh Amit Kumar Singh Swati Nupur Srivastava Sandeep Singh A. K. Chowdhary 《Environmental Earth Sciences》2010,59(8):1703-1715
In the northern part of the Indian sub-continent, the Gomati River (a tributary of the Ganga River) was selected to study the dynamics of Arsenic (As) mobilization in fluvial environment of the Ganga Plain. It is a 900-km-long, groundwater-fed, low-gradient, alluvial river characterized by monsoon-controlled peaked discharge. Thirty-six water samples were collected from the river and its tributaries at low discharge during winter and summer seasons and were analysed by ICP-MS. Dissolved As and Fe concentrations were found in the range of 1.29–9.62 and 47.84–431.92 μg/L, respectively. Arsenic concentration in the Gomati River water has been detected higher than in its tributaries water and characteristically increases in downstream, attributed to the downstream increasing of Fe2O3 content, sedimentary organic carbon and silt-clay content in the river sediments. Significant correlation of determination (r 2 = 0.68) was also observed between As and Fe concentrations in the river water. Arsenic concentrations in the river water are likely to follow the seasonal temperature variation and reach the level of World Health Organization’s permissible limit (10 μg/L) for drinking water in summer season. The Gomati River longitudinally develops reducing conditions after the monsoon season that mobilize As into the river water. First, dissolved As enters into pore-water of the river bed sediments by the reductive dissolution of Fe-oxides/hydroxides due to microbial degradation of sedimentary organic matter. Thereafter, it moves upward as well as down slope into the river water column. Anthropogenically induced biogeochemical processes and tropical climatic condition have been considered the responsible factors that favour the release of As in the fluvial environment of the Ganga Plain. The present study can be considered as an environmental alarm for future as groundwater resources of the Ganga–Brahmaputra Delta are seriously affecting the human–environment relationship at present. 相似文献
998.
The present study deals with locally rotationally symmetric (LRS) Bianchi type II cosmological model representing massive
string. The energy-momentum tensor for such string as formulated by Letelier (Phys. Rev. D 28:2414, 1983) is used to construct massive string cosmological model for which we assume that the expansion (θ) in the model is proportional to the shear (σ). This condition leads to A=B
m
, where A and B are the metric coefficients and m is proportionality constant. For suitable choice of constant m, it is observed
that in early stage of the evolution of the universe string dominates over the particle whereas the universe is dominated
by massive string at the late time. Our model is in accelerating phase which is consistent to the recent observations of type
Is supernovae. Some physical and geometric behavior of the model is also discussed. 相似文献
999.
K. Naha C. S. Venkitasubramanyan R. P. Singh 《International Journal of Earth Sciences》1968,58(2):929-950
In the Early Precambrian Banded Gneissic Complex between Amet and Lawa Sardargarh in central Rajasthan, India, open to isoclinal upright folds with NNE-striking axial planes have affected westerly plunging isoclinal folds of reclined, inclined and rare upright attitudes. Interference patterns of diverse shapes ranging in scale from inches to miles have been caused by variable angle between the axes and axial planes of the early folds, angular variation in the attitudes of the two fold systems, and spatial variation in the tightness of the later folding.
Zusammenfassung In dem früh-präkambrischen gebänderten Gneißkomplex zwischen Amet und Lawa Sardargarh in Mittel-Rajasthan, Indien, haben offene bis isoklinale, senkrechte Falten mit NNE-streichenden Axialflächen nach Westen abtauchende isoklinale Falten überprägt, die selbst eine geneigte, überkippte oder seltener senkrechte Lage aufweisen. Überlagerungsmuster von unterschiedlicher Form und Größe (von Zoll bis zu Meilen) wurden verursacht durch 1. verschiedene Winkel zwischen den Achsen und den Axialflächen früherer Falten, 2. Winkelveränderungen in der Anordnung der zwei Faltensysteme und 3. räumliche Veränderungen in der Dichte der späteren Faltung.
Résumé Dans l'ensemble de gneiss zoné du Précambrien inférieur entre Amet et Lawa Sardargarh, à Rajasthan central aux Indes, des plissements ouverts à isoclinaux, de direction NNE, ont affecté des plissements isoclinaux reclinés, inclinés ou rarement verticaux, plongeant vers l'ouest. Des patrons d'interférence de formes diverses, à l'extension d'un centimètre au kilomètre, ont été causés par des angles variables entre les axes et les surfaces axiales des premiers plissements, des variations angulaires dans la disposition des deux systèmes de plissement, et des variations d'espace des plissements postérieurs.
(). _ .相似文献
1000.